Hello Guys,
I have setup a simple remote access concept for my Home Assistant. I have a DDNS service running on my Synology NAS. On my router I setup simple port forwarding for port 8123 to my Home Assistant raspberry Pi. And when I try to connect to the DDNS URL including the right port I do get the initial logon screen, but directly after it shows me the “Anable to connect to Home Assistant” screen. 
To another raspberry in my own network this port forwarding method does work without problems.
Does anyone have any solutions for this?